[Denmark, USA] They’re possibly the tiniest, most ancient gardeners in the world. A type of marine bacteria tends algae, using pesticides to keep other microbes away.
Understanding how Roseobacter does this could help us better understand nutrient circulation in the world’s oceans, where the bacteria and their microalgae “crops” are abundant.
“They’re key players in global nutrient recycling,” says Eva Sonnenschein of the Technical University of Denmark in Lyngby, who reported her team’s latest results last month at the annual meeting of the American Society for Microbiology in Boston. On average Roseobacter account for 3 per cent of bacterial diversity globally, and as much as 20 per cent in places.
Both the bacteria and the algae appear to benefit from the arrangement, reminiscent of ants farming aphids. “I suspect it’s mutualism,” says Rita Colwell of the University of Maryland at College Park. “They wouldn’t be there if it wasn’t beneficial to both parties.”
When times get tougher, though, and the algae begin competing with the bacteria for resources, the “farmers” stop making antibiotics and instead produce a substance that kills off the algae, harvesting the rich algal decay products.
Microbes with tools
Sonnenschein’s team has now investigated the “tools” that the bacteria use to manage their algal gardens. These include a “herbicide”, tropodithietic acid (TDA), which protects the algae from other bacteria, and roseobacticides, the substances that kill off the algae for harvest.
The team studied samples from aquaculture facilities in Denmark, Spain and Greece and from seawater off the coast of Denmark, Germany and Australia. They identified and studied strains of a particular species of Roseobacter called Phaeobacter inhibens, most of which produced roseobacticides.
By comparing their genomes with those of the strains that did not, the researchers could home in on genes likely to be responsible for their production. They found that the microbes that make TDA aren’t always also able to produce the compounds that kill algae. Indeed, they identified 41 gene clusters that are unique in those bacteria that can make roseobacticides.
It is thought that algal breakdown products induce more production of roseobacticides, creating a positive feedback loop that causes more algae to be killed off.
Sonnenschein and her colleagues are now trying to gauge the environmental impact of the algal farming, and the factors that dictate whether the bacteria protect or harvest the algae. “We’re doing experiments battling the two against each other,” she says.
View original article at: Bacteria ‘gardeners’ farm algae to harvest when food runs out